Feedback in audio systems is caused by the output signal coupling to an input through an acoustic path, creating a regenerative signal in the loop that results in an undesirable sound. It occurs in all types of systems, from simple public address systems to sophisticated wireless radio communication systems. The conventional ways of dealing with feedback sound include several approaches. One approach is physically separating the input (e.g. microphone) and the output (e.g. speaker) sufficiently to prevent the regenerative signal from occurring. Of course, this is not always possible. Another approach is to simply apply a notch filter at the feedback frequency. This approach is only effective if the feedback occurs at a known frequency, or if the frequency is determined and then a corresponding filter applied, and if the filter doesn't unduly affect the frequency content of desired signals. However, in more complex systems there can be various types of feedback occurring at different frequencies, with different characteristics. Pre-emptively inserting filters to address all forms of feedback would not be practical. Since feedback is regenerative, another approach that is often used is to vary the pitch of audio signals to prevent the regenerative effect from occurring. Pitch can either be shifted to avoid a known resonance frequency or frequency band, or the fundamental pitch of a sound can be determined and varied above and below the fundamental pitch. Pitch shifting is effective, but can often be detected by a listener and is thus not an optimum solution. Other methods include simply detecting a strong tone-like signal in the audio spectrum of the signal through the system and responding by lowering volume, or applying a notch filter at the feedback frequency. This, however, presumes feedback is occurring, which means that listeners are hearing feedback by the time the system detects and applies a measure to address the feedback.
All of the conventional methods are effective, but have their drawbacks. They either require identifying feedback as it occurs, meaning it is being heard by the time it is detected, or requires foreknowledge as to the frequency so that a selected filter can be applied.
Accordingly, there is a need for a method and apparatus for suppressing feedback in an audio system that operates faster than conventional methods and in an adaptive manner to address different kinds of feedback.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.